1. Field of the Invention
The present invention relates to a balancing apparatus utilizing an ultraviolet hardening agent and a ball for preventing a rotating member that is rotated at a super high velocity such as a VTR head driving apparatus, a laser scanning unit and the like, from being vibrated or oscillated due to an imbalance generated by inequality in the material and the shape of the rotating member.
2. Description of the Related Art
As widely known, a balancing apparatus is provided to remove an imbalance generated due to inequality of the material density of and incomplete circular shape of a shaft that is rotated at a super high velocity. The balancing apparatus includes a ring-shaped hoop installed on the shaft, a ball freely moved in the hoop and an operational fluid introduced into the hoop, for preventing the ball from being suddenly moved and removing a minute rotational imbalance. When the shaft is rotated at a velocity higher than a critical velocity thereof, the ball and the fluid of the balancing apparatus are automatically located at a position where the eccentricity is compensated. The critical velocity is a velocity when the eccentricity begins to be compensated for by the ball and the operational fluid.
A conventional VTR head driving apparatus including such a balancing apparatus for removing such as an imbalance will be described with reference to FIG. 1 hereinafter.
FIG. 1 shows an upper drum 20 which a head tip 10 for reading audio and video signals written on a VTR tape is fixed to.
The upper drum 20 is connected to a rotation power generating unit (not shown). A ring-shaped groove 30 having a little smaller diameter than the upper drum 20 is formed in an upper surface of the upper drum 20. A predetermined number of balls 40 that are solid balancers having a predetermined density are inserted into the groove 30. A fluid 50 that is a liquid balancer having a predetermined density is also introduced into the groove 30. The fluid 50 prevents the balls 40 from being suddenly moved and adjusts a minute imbalance generated on the upper drum 20.
The amount of the fluid 50 introduced into the groove 30 is, preferably, ranged from 1/3 to 1/2 of the ring-shaped groove 30.
An opening of the ring-shaped groove 30 including the balls 40 and the fluid 50 is closed by a cover 60 for preventing the balls 40 and the fluid 50 from flying out of the groove 30. The cover 60 has a shape that is similar to and larger than the opening of the groove 30.
The operation of the conventional balancing apparatus will be described hereinafter.
First, when power is supplied to a rotation power generating unit (not shown), the upper drum 20 begins to be rotated in association with a shaft A connected to the rotation power generating unit. The rotations per minute of the upper drum 20 increase according to an increase in the angular acceleration of the rotation power generating unit. After a predetermined amount of time, the upper drum 20 is rotated at a constant velocity ranging from 4000 to 9000 R.P.M.
However accurately and precisely the upper drum 20 is fabricated, when the upper drum 20 is rotated at a super high velocity, several milligrams of imbalance is inevitably generated on the upper drum 20 due to a minute asymmetry in the shape of and inequality of the material density of the upper drum 20. The imbalance is compensated for by the balls 40 and the fluid 50 of the balancing apparatus formed in the upper drum 20, in such a manner that the balls 40 and the fluid 50 are moved to a position that is symmetrical to a position that the imbalance is generated. This results in an enhanced rotation stability of the upper drum 20.
The balls 40 and the fluid 50 of the conventional balancing apparatus are capable of compensating for only the imbalance generated when the rotating member, i.e. the upper drum 20, is rotated at a velocity that is higher than a critical velocity of the upper drum 20. Accordingly, the imbalance compensating ability of the conventional balancing apparatus is considerably reduced when the rotating member is rotated at a velocity that is lower than the critical velocity. As a result, the performance and the life of the rotating member may be also reduced because the rotating member may be vibrated and oscillated by the rolling movement of the balls until a rotating velocity of the rotating member reaches the critical velocity of the rotating member.